This invention relates to invalid positioning devices and particularly, but not exclusively, to an invalid positioning device for use with slings in which invalids are suspended during lifting.
Invalid positioning devices having a lifting element pivotable about a main horizontal axis are well known. These devices typically come in two types. One type acts as a standing aid for a patient and the other type utilises a full-body sling by which the patient can be completely suspended from the device. Typically, the lifting elements of both types of device are power operated by rotary or linear drive means.
One drawback associated with the use of rotary drive means is that a rotary actuator only produces a constant torque and the lifting element will thus only be pivotable at a constant angular speed over its range of angular displacement.
A further drawback lies in the fact that rotary actuators which are able to produce a sufficient amount of torque while not being too oversized have to be purpose built and as such are not cost-effective.
Yet a further drawback exists when using a rotary actuator in the second type of invalid positioning device, such as is known from GB-A-2127931. In this type of arrangement, the rotary drive means is housed adjacent to the horizontal axis about which the lifting element, in the form of a sling hanger, pivots. This causes problems when the sling hanger is presented with fluids, such as in the case when an invalid patient is lowered into a bath of water. Although some water proofing means can be applied, this will invariably be inadequate and undesirable seepage and contact will still occur.
A drawback associated with the use of linear drive means is that a lifting element, operated via a linear actuator incorporated in the linear drive means, typically exhibits its greatest angular speed about the main horizontal axis when at the ends of its range of angular displacement, and typically exhibits a maximum torque in the region of the mid-point of its range of angular displacement.
The present invention seeks to provide an invalid hoist which overcomes these drawbacks.
According to one aspect of the present invention, there is provided an invalid positioning device comprising a support structure, a lifting element angularly displaceable about a main horizontal axis relative to the support structure between two extreme positions and a power operated mechanism for pivoting the lifting element about said main horizontal axis, the power operated mechanism being arranged such that the torque applied by the power operated mechanism decreases as the lifting element moves away from one extreme position and increases again as the lifting element approaches its other extreme position and such that the angular speed of the lifting element increases as it moves away from one extreme position and decreases as it approaches its other extreme position.
According to a second aspect of the invention, there is provided an invalid positioning device comprising a support structure, a lifting element angularly displaceable about a main horizontal axis relative to the support structure between two extreme positions and a power operated mechanism for pivoting the lifting element about said main horizontal axis, wherein the power operated mechanism comprises an actuator and a lever, a first part of which is supported for pivotable movement relative to the support structure about a second horizontal axis spaced from said main horizontal axis and a second part of which is connected to the lifting element by a slidable connection which moves closer to said main horizontal axis as the lifting element moves away from one extreme position towards an intermediate position and then moves away from said main horizontal axis as the lifting element moves from said intermediate position towards its other extreme position.
The invention will now be more particularly described, by way of example, with reference to the accompanying drawings.